Electrical and electromechanical system employing magnetostrictive devices



Aug. 22, 1939. R MASON 2,170,206

ELECTRICAL AND ELECTROMECHANICAL SYSTEM EM PLOYING MAGNETO-STRICTIVE DEVICES Filed May 8, 1937 3 Sheets-Sheet l FIG. 2

REACTANC'E Q I g I FREQUENCY 32 26 E 2 F 6 X 2" f E 6 3 2 g '41 so 26 E 0 FREQUENCY E X] l I I $50- I 2' Q I I l V i 2ol" I I I EZ' I l I FREQUENCY INVENTOR 8 g F. ZASON A TTORNE Y Aug. 22, 1939. v w ON 2,170,206

ELECTRICAL AND ELECTROMECHANICAL SYSTEM EMPLOYING MAGNETOSTRICTIVE DEVICES Filed May 8, 1937 s Sheets-Sheet 2 FIG.

REA C TIM/CE FIG. /2

mam MOUNTING S I 0 A TTENUA Tram-"d FREQUENCY FIG. /5A F/G.

M/VEN TOR W PMASON A 7 TOR/VE'V Aug. 22, 1939. MASON 2,170,206

ELECTRICAL AND ELECTROMECHANICAL SYSTEM EMPLOYING MAGNETOSTRICTIVE DEVICES Filed May 8, 1957 3 Sheets-Sheet 3 F/G. Z/

'0 U E 3 E F/GIZZ Q 2 5 Q i E k 0 FREQUENCY me h I 24 s7 Z5 96 l57 /02 195 I03 2 l 98 F3797 58 7 I /N 1 5 N TOR Patented Aug. 22, 1939 iJNi'iE V stares CFHQE ELECTRICAL AND ELECTROMECHANICAL SYSTEM EMPLO'YING MAGNETOSTRIC- TIVE DEVICES Application May 8, 1937, Serial No. 141,485

10 Claims.

This invention relates to the use of magnetostrictive devices in electrical and electromechanical systems.

In a copending application of, E. Lakatos, Serial No. 133,837 of March 30, 1937 it is shown that by suitable construction and design magnetostrictive devices may be produced which will have highly reactive characteristics and relatively small dissipative tendencies.

It is an object of this invention to utilize magnetostrictive devices of the type described in the above-mentioned copending application to particular advantage in reactive systems.

Another object of this invention is to provide new means of converting electrical energy, distributed over a wide range of frequencies, into acoustic or mechanical energy of corresponding frequency distribution with relatively small attenuation and distortion of the energy within said range of frequencies.

A further object is to provide methods of cooperatively associating magnetostrictive devices with non-magnetostrictive devices and methods of extending the field of usefulness of magnetostrictive devices.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the accompanying drawings:

Fig. 1 shows an equivalent electrical network of a magnetostrictive device of the type contemplated in this invention;

Fig. 2 shows the electrical reactance of the device of Fig. 1;

Fig. 3 shows an equivalent electrical network of a magnetostrictive device in series with an electrical condenser;

Fig. 4 shows the electrical reactance of the combination of Fig. 3;

Fig. 5 shows the equivalent electrical network of a magnetostrictive device in parallel with" an electrical capacity;

Fig. 6 shows the electrical reactance of the combination of Fig. 5;

Fig. 7 shows the equivalent electrical network of a T section of a ladder type filter employing magnetostrictive devices as reactive arms thereof;

Fig. 8 shows the recurrent series (Z1) and recurrent shunt (Z2) reactance-frequency diagrams for the structure of Fig. '7

Fig. 9 shows the attenuation frequency char acteristic of the structure of. Fig. 7;

Fig. 10 shows a filter section of lattice type employing combinations of the type shown in Fig. 5;

Fig. 11 shows recurrent series (Z1) and recurrent shunt (Z2) reactance-frequency diagrams for the structure of Fig. 10;

Fig. 12 shows the attenuation-frequency characteristic of thestructure of Fig. 10;

Fig. 13 shows in diagrammatic form an electromechanical system employing magnetostrictive elements to actuate a loud-speaker dia- Dhragm;

Fig. 14 shows an electrical representation in schematic form of the system of Fig. 13;

Figs. 15A and 15B are illustrative of the process of transformation from electrical into mechanical energy involved in the system of Fig. 13;

Figs. 16 and 17 are refinements of the system a]: Fig. 13 which facilitate the analysis of the latter;

Fig. 18 shows the all-electrical equivalent net work of the system of Fig. 13 with an electrical condenser in series therewith;

Fig. 19 shows the equivalent lattice structure for Fig. 18 without the series condenser;

Fig. 20 shows the equivalent lattice structure for Fig. 18;

Fig. 21 shows the recurrent series (Z1) and recurrent shunt (Z2) reactance-frequency diagrams for the structures of Figs. 19 and 20;

Fig. 22 shows the attenuation frequency characteristics of the structures of Figs. 19 and 20;

Fig. 23 shows an alternative form of loudspeaker of the same general class as that of Fig. 13 but employing a horn;

Fig. 24 shows an electrical representation in schematic form of the system of Fig. 23;

Fig. 25 shows the schematic of the system of Fig. 24 transformed to an equivalent all-electrical system;

Fig. 26 shows a system of this invention suitable for use as a submarine sound radiator.

It is shown in the copending application of E. Lakatos mentioned above that magnetostrictive devices may be constructed to simulate the impedance of an electrical network of the type shown in Fig. 1, inductance 26 representing the damped inductance of the device and the antiresonant combination of inductance 28 and capacity 38 representing the motional impedance. In the device disclosed by Lakatos the resistive components 21 and 29 are suficiently small that the reactive characteristics may for the majority of practical purposes be assumed to be those 01 a dissipationless network.

The reactive characteristics of a nearly dissipationless network of the type of Fig. 1 are shown in Fig. 2. As explained in the copending application of E. Lakatos mentioned above, the separation between the so-called critical frequencies, that is, the anti-resonant frequency 1 and the resonant frequency f2 is a function of the coupling factor k of the magnetostrictive device and under some circumstances it becomes difiicult if not impossible to obtain a sufiiciently large coupling factor to permit thedesired spacing of the critical frequencies.

However, when magnetostrictive devices are employed in conjunction with electrical capacities, not only is an additional critical frequency provided by the combination, but also the frequency spacing between the critical frequencies of the magnetostrictive device is increased.

Figs. 3 and 5 show series and parallel combinations, respectively, of'an electrical capacity and a magnetostrictive device and Figs. 4 and 6 show the respective reactive. characteristics of these combinations.

In Fig. l we find a new resonant frequency is and a greater separation between the critical frequencies f1 and f2 contributed by the magnetostrictive device than occurs with the magnetostrictive device alone as illustrated in Fig. 2. This efiect is obviously the result of resonance between the damped inductance of the magnetostrictive device and the added capacity 32. The anti-resonance f1 will occur at the same frequency as for the device alone, that is at f1. The new resonance f3 will occur below the anti-res onance and the resonance )2 of the device alone will occur at a higher frequency, f2 for the combination.

Similarly, .in Fig. 6 we find a new anti-resonance is occurring above the resonant frequency f2, the latter being at the same frequency as the resonance f2 of the device. alone. The antiresonance ii of the device, however, is moved down to frequency ii" of the combination, as shown.

By means of the reactance theorem described by R. M. Foster in the Bell System Technical Journal, volume 3, No. 2, April 1924:, pages 259 to 267, the values of the various elements including those representing the equivalent network of the magnetostrictive devices may be ca-lculatedand additional elements may be added to provide more complex reactive networks.

That complex networks of reactive elements may take any one of a number of equivalent forms is demonstrated in an article entitled Mutual inductance in wave filters with an in troduction on filter design. by K. S. Johnson and T. E. Shea in the Bell System Technical Journal, vol. 4, No. 1,-January 1925, pages 52'to 83. This article also shows numerous methods of employing such complex reactive networks as component arms of electrical wave filters of the ladder type and on page 83 sets out relations by which'equivalent lattice or bridge T type filter sections may be obtained. As will appear hereinafter it is frequently advantageous in analyzing a ladder type network to examine the properties of its equivalent lattice type section.

Fig. 7 of theaccompanying drawings shows a T section of ladder typefilter in which the three arms are magnetostrictive. devices. Fig. 8 shows the relation between the full recurrent series arm reactance X1 and the full recurrent shunt arm rea-ctance X2, for this type of filter, 4X2 is plotted to facilitate analysis of the attenuation characteristics of the filter in accordance with wellknown. principles. Fig. 9 shows the attenuation of the filter section of Fig. 7. (In the T section shown in Fig. '7, according to well-known theory, each series. arm is and the shunt arm is Z2 unless special terminations to improve impedance or permit use in parallel with other networks are employed.)

Similarly, Fig. 10 shows a lattice type filter section employing four combinations of the type shown in Fig. 5. The series arm, shunt arm, reactances X1 and X2, respectively, are shown. in Fig. 11 and the attenuation of the filter section of Fig. 10 is shown in Fig. 12. U. S. Patent 1,828,454 issued November 20, 1931 to H. W. Bode and numerous other well-known publications give a thorough. analysis of lattice type networks.

Numerous other combinations of magnetostrictive devices with non-magnetostrictivedevices whose electrical reactive properties are suitable may obviously be made. Electrical networks of numerous varieties designed in accordance with well-known principles, can therefore employ magnetostrictive devices alone, and in suitable combinations, 'to advantage;

For example, from the equivalent electrical network or a magnetostrictive device it is apparent that it may,,for a number of purposes, be considered as having reactive properties potentially the inverse of those of a piezoelectric crystal. This at once suggests that the two devices may be advantageously combined to realize reactive networks of numerous varieties.

Generally speaking, the frequency range of greatest usefulness is somewhat lower for magnetostrictive devices than for piezoelectric devices so that over certain intermediate frequency bands complex networks employing both devices severally and in combination as arms thereof appear entirely practicable. The principles involved are, of course, the same as would govern the use of the equipment combinations of simple electrical elements in purely electrical networks,

and are well known.

as the medium of converting electrical energy into acoustic or mechanical energy. It will now be shown that, by building out the electrical circuit the over-all transmitting characteristics of a properly proportioned electromechanical systern employing a magnetostrictive device of the type contemplated may be made that of a wide band electromechanical wave filter. Fig. 13 shows in diagrammatic form such an electromechanical system. It comprises the electrical capacity 64 in series with the electrical, coil 94. Within the coil are assembled about a centrally located polarizing magnet 92 a convenient number of magnetostrictive elements 9|, the magnet and elements conforming with the requirements described in the above-mentioned application of E. Lakatos. At the left end, as shown in- Fig. 13, these elements and the magnet are held by the rigid support At the right end the elements are attached to the diaphragm 95.. Sufficient clearance is left between the diaphragm and the right end of magnet 92 to avoid any interference with the motion of the former.

Fig. 14 shows in schematic form an elementary electrical representation for such an electro-magnetostrictive-mechanical filter by means of which electrical energy E; supplied to the input terminals of the magnetostrictive device is converted into mechanical force and applied to drive a mechanical resistive load 65. Resistive load 55 may be for example the loud-speaker, radiating diaphragm of Fig. 13. In Fig. 14, resistance 56 represents the mechanical energy dissipation of the device exclusive of the mechanical load, inductance 55 represents the equivalent of the mechanical mass, capacity 54 represents the equivalent of the mechanical stiffness, negative series reactances 52 and positive shunt reactance 53, all three of which have the value a'M, where M is the coupling impedance between the electrical and pendent of frequency, taken together represent mechanical portions of the system and is indethe equivalent of the electromechanical transformer action of the device, inductance 5i represents the damped inductance of the electrical coil of the device and resistance 50 represents the electrical energy dissipation of the device. All of the elements appearing in Fig. 14 can be determined by direct electrical and mechanical measurements.

The resistance 58 and inductance 5| are the Values which will be measured on the electrical side if the mechanical side is clamped or prevented from moving. This is equivalent to making the resistance 65 infinite, in which case it is readily seen that the impedance on the electrical side is the resistance 50 and the inductance 5 I.

On the other hand, the equivalent capacity 54, inductance 55 and resistance 56 can be measured by mechanical means when the electrical portion of the circuit is left open. The capacity 54 is the inverse of the stiffness of the magnetostrictive element (or elements taken collectively if several are employed as in Fig. 13) the inductance 55 is the value required to resonate the capacity 54 at the resonant frequency of the magnetostrictive element, and the resistance 56 is the resistance measured at the resonant frequency of the magnetostrictive element.

All the quantities are accordingly determined except the coupling impedance giM. To determine this we oppose the motion of the magnetostrictive element by a force F when we send a known current in through the electrical coil. It is then obvious that the ratio of the force on the mechanical side, which is just sufficient to prevent motion, to the current flowing in the electrical circuit will be equal to M, the absolute value of the coupling impedance. This ratio is often called the force factor of the system.

By the measurements just described the equivalent electrical schematic representation of a system, such as that diagrammatically represented in Fig. 13, may be completely determined.

The nature of the electromechanical transformer action of an electromagnetic device is explained in detail in U. S. Patent 1,681,554 issued to E. L. Norton on August 21, 1928. Since a magnetostrictive device is an electromagnetic device the reactive properties of which are accentuated and modified by the magnetostrictive activity of its core the analysis applies equally well to it provided the effects of the magnetostrictive activity are taken into account. In accordance with Nortons analysis the electromechanical transformer comprising negative series reactances 52 and positive reactance 53 may be replaced as illustrated in Figs. 15A and 153 by an idwl transformer 59 having the appropriate impedance ratio and havingits input shunted by an impedance 58. The conception designated by the term ideal transformer is well known and is explained in numerous publications including the book by K. S. Johnson entitled Transmission Circuits for Telephonic Communication, Chapter VI, the fourth printing of which was published in 1929 by D. Van Nostrand Company of New York city.

From the nature of the electromechanical conversion efiected by the magnetostrictive device it follows that where is the ratio of transformation, w=21rf, f: frequency of the applied voltage, Lo=electrical inductance 5|, and Civr=mechanical stiffness 54.

The equivalent T of the ideal transformer 59 and shunting impedance 58 represented by impedances 6!, 52 and 63 of Fig. 153 may be derived as shown in the above-mentioned patent to E. L. Norton. To make impedance 83 equal 7M, thatis the mutual impedance between the electrical and mechanical systems, impedance 58 must equal the quantity This results in making impedance 6| equal to the quantity and impedance 62 equal to the quantity W O M For a given magnetostrictive device the quantity 1 L0 is a constant which will be designated as k. This is the constant k donated by Lakatos in his abovementioned application as the coupling factor.

Replacing the electromechanical coupling device of Fig. 14 by the equivalent T structure derived above for Fig. 153 and combining like series elements we obtain Fig. 16 in which inductance 5? equals LOU-l0), impedance 58 equals Lok and condenser 68 equals Neglecting for the present the electrical and mechanical dissipations represented by resistances 50 and 58 respectively, the system of Fig. 17 is obtained. As explained in the above-mentioned application of E. Lakatos these dissipations may be safely neglected if reasonably small since in such a case their effects upon the reactive properties of the network are slight. For the system of Fig. 17 the mesh equations are where i1 is the input current, E1 is the primary Equations 9 and 8 may respectively be rewritten in the form A, B, C and. D being the coefiicients shown in Equations 9 and 8 respectively. I By well-known principles for any dissymmetrical filter To make (1) constant at all frequencies requires the further restriction that and the expression for the image transfer constant becomes 1 m. cosh 6 (18) Thecut-off or limiting frequencies of the transmitted band occur when cosh 9::1 and are In Equations 18, 19 and 20 subscript m refers to the mid-band frequency, aim being 21rfm and fm being said mid-band frequency.

The image impedances of the filter are and 1 .2 z 2 (1) I zl 1+( 2+ mm (22) At the mid-frequency where w wm the image impedances are If the magnetostn'ctive member is free to vibrate theresulting impedance, equivalent to the short-circuited impedance of an all-electrical network,' may be calculated by making E0=0.

The'band width of the filter is therefore the same as the distance between the resonant points of the combination of Fig. 3 consisting of a mago o k netostrictive device in series ,with a condenser.

In the above analysis the inversion of the electrical equivalents of the mechanical portion of the system necessary to produce an equivalent Fig. 17, inductance I0, condenser 75 and resistance 80 being now electrical elements the inverse of the mechanical stiffness 60, the mechanical mass and the mechanical resistive load respectively, modified by the ratio r to allow for the impedance change introduced by transformer 59. 7

Figs. 19 and 20 are lattice structures here introduced to facilitate analysis of the effect of adding series condenser 64 to the system represented by Fig. 18. Fig. 19 shows the equivalent lattice of the system of Fig. 18 without condenser 64 and Fig. 20 showsthe equivalent lattice of the complete system shown in Fig. 18. The relations between the-elements of the structures of Figs. 18, 19 and 20 aregiven' on page 83 of the above-mentioned paper by Johnson and Shea.

Fig. v21, curves I8 and .19 are the recurrent shunt arm reactance-frequency characteristics for the structure of Fig. 19 and curves 8i and 82 are the corresponding characteristics for the structure of Fig.20.

Fig. 22, curves 83 and 84 showcomparatively the attenuation-frequency characteristics of the structures of Figs. 19 and 20 respectively. The diiference between these characteristics represents effect of adding series capacity 64 to complete the system of Fig. 18. The increase in band width so obtained may,.in not unusual instances,

be in .the order of tenfold.

Fig. 23 shows ,a loud-speaker similar to that of Fig. 13 except for the addition of a horn I00 which clamps the outer periphery of the diaphragm. ,Fig. 24 indicates the modification of the electrical schematic representation of'the mechanical system comprising mainly shunt ca'' pacitance {0| (mechanical elastance) introduced by the necessity of flexing the diaphragm and on the electrical side the anti-resonant combination comprising inductance 98 and capacity 91 necessary inithis instance .in addition to the series capacity 9-6 to complete. the building out of' the system to the equivalent of a wide band allelectrical wave filter. Fig. 24 shows the schematic of the system converted to the all-electrical equivalent filter as explained above, the shunt mechanical elastance Hll becoming in the allelectrical system the series inductance I02.

Fig. 26 shows a plurality of magnetostrictive units of the type described in connection with Fig. 13 employed to drive a submarine radiator By means of a series capacity I08 the system may be built out to a wide-band electrical wave filter in the same manner as was the system of Fig. 13.

Numerous other arrangements within the spirit and scope of the invention may obviously be made and no attempt has here been made to be eX- haustive.

What is claimed is:

1. In combination a magnetostrictive device comprising a single electrical coil electromagnetically coupled with a single vibrating element of magnetostrictive material, and a condenser in series with said electrical coil whereby said com,- bination produces at one frequency an electrical anti-resonance and at two other frequencies electrical resonances, the anti-resonance occurring at a frequency lying between the frequencies at which resonance occurs, all of said frequencies being non-harmonically related.

2. In combination a magnetostrictive device comprising a single electrical coil electromagnetically coupled with a single vibrating element of magnetostrictive material, and a condenser in parallel with said electrical coil whereby said combination produces at one frequency an electrical resonance and at two other frequencies electrical anti-resonances, the resonance occurring at a frequency lying between the frequencies at which'the anti-resonances occur, all of said frequencies being non-harmonically related.

3. An electrical wave filter comprising a plurality of impedance branches arranged between a pair of input terminals and a pair of output terminals. to form a lattice network each lattice branch of said network including a magnetostrictive device in combination with a capacity, the reactances of the branches being proportioned. with respect to each other toprovide a single transmission band.

4. An electrical wave filter comp-rising a plurality of impedance branches arranged between a pair of input terminals and a pair of output terminals to form a T network, each impedance branch consisting of a magnetostrictive device, the reactances of the branches being proportioned with respect to each other to provide a single transmission band.

5. An electrical wave filter comprising a plurality of impedance branches arranged between a pair of input terminals and a pair of output terminals, a number of said branches bearing a series relation to the transfer of energy through said filter and the remainder bearing a shunt relation to said energy transfer, said remainder of impedance branches each including a magnetostrictive device, the reactances of all said branches being proportioned with respect to each other to impart definite predetermined transmitting, impedance and phase characteristics to said filter.

6. An electrical wave filter comprising a plurality of impedance branches arranged between a pair of input terminals and a pair of output terminals, a number of said branches bearing a series relation to the transfer of energy through said filter and the remainder bearing a shunt relation to said energy transfer, said first number of impedance branches each including a magnetostrictive device, the reactances of all said branches being proportioned with respect to each other to impart definite predetermined transmitting, impedance and phase characteristics to said filter.

'7. An electrical wave filter comprising a plurality of impedance branches arranged between a pair of input terminals and a pair of output terminals, a number of said branches bearing a series; relation to. the transfer of energy through said filter and. the remainder bearing a shunt relation to said energy transfer, a portion of said branches each including in combination a magnetostrictive device and a capacity, the reactances of all said branches being proportioned with respect toeach other to impart definite predetermined transmitting, impedance and phase characteristics. to said filter.

8. An electromechanical system comprising a magnetostrictive device arranged to drive a sound radiating device, an electrical capacity connected in series with the electrical coil of said magnetostrictive device and an electrical anti-resonant impedance connected in parallel with the series combination of said capacity and said coil, the impedances of all said component parts being so proportioned relative to each other that said system provides substantially distortionless wave transmission of energy, involving the conversion of electrical to acoustic energy, over a. wide range of frequencies.

9. A magnetostrictive device including an electrical coil, a core of magnetostrictive material and a magnetizing member, said core being divided into a plurality of portions, said portions being assembled about said magnetizing member, the assembly so formed being inserted centrally through said coil whereby polarization of the core portion is attained while at the same time magnetic shielding of said magnetizing member from said coil and close coupling between said coil and said core portions are effected.

10. A magnetostrictive vibrator comprising a plurality of independent vibrating elements of magnetostrictive material, a polarizing member for said vibrating elements and an electrical coil enclosing all of said elements and said polarizing member, said vibrating elements being positioned between said coil and said polarizing member whereby said elements tend to magnetically shield said polarizing member from said coil thereby reducing electromagnetic coupling between said polarizing member and said coil.

WARREN P. MASON. 

